Mesa, Arizona (CNN) - Rick Santorum found that his position at the top of polls made him the biggest target in Wednesday's CNN Republican presidential debate, possibly the last of the GOP primary and caucus campaign.

Mitt Romney, who has been front-runner off and on through the campaign but saw his momentum blunted by Santorum's recent surge, went after the former Pennsylvania senator over his record in Congress, trying to shoulder past him before Tuesday's primaries in Arizona and Michigan, which most polls show neck-and-neck between the two.